如何解决实体框架核心System.ArgumentNullException

Question

从下面的堆栈跟踪中，我无法分辨错误消息的错误。我用--verbose标志运行了迁移命令，希望它有助于查明问题，但是zilch。

  dotnet ef migrations add migwl3 --verbose

我找不到名为key的参数

  System.ArgumentNullException: Value cannot be null.
  Parameter name: key
   at Microsoft.EntityFrameworkCore.Utilities.Check.NotNull[T](T   value, String parameterName)
   at     Microsoft.EntityFrameworkCore.SqlServerMetadataExtensions.SqlServer(IKey key)
   at    Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.    <Add>d__41.MoveNext()
   at System.Linq.Enumerable.<CastIterator>d__35`1.MoveNext()
   at System.Linq.Enumerable.Single[TSource](IEnumerable`1 source)
   at     Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.   <Add>d__29.MoveNext()
   at     Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.   <DiffCollection>d__56`1.MoveNext()
   at System.Linq.Enumerable.ConcatIterator`1.MoveNext()
   at      Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.S      ort(IEnumerable`1 operations, DiffContext diffContext)
  at      Microsoft.EntityFrameworkCore.Migrations.Design.MigrationsScaffolder.Scaf      foldMigration(String migrationName, String rootNamespace, String      subNamespace)
   at     Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMig      ration(String name, String outputDir, String contextType)
  at      Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(S    tring name, String outputDir, String contextType)
  at     Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
  at     Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Exec     ute(Action action)
 Value cannot be null.
 Parameter name: key

关于如何解决问题（项目编译正常）的任何提示将不胜感激

Answer 1

这是搜索Microsoft.EntityFrameworkCore.Utilities.Check.NotNull的第一个结果之一，所以我将添加我的愚蠢错误：

我为不同的DatabaseContext重构了一个类，然后在来自不同上下文的两个Join查询之间调用IQueryable--显然你不能在EntityFramework中做到这一点

Answer 2

我认为你的问题是你的模型，你不装饰[Key]属性或不使用HasKey。请分享您的代码。